1. Field of the Invention
A dual collimator for beat-to-beat measurement of cardiac performance with an Anger camera.
2. Description of the Prior Art
A number of nuclear medicine methods are available for the evaluation of cardiac performance, but few are applicable to beat-to-beat studies. Multigated Anger-camera acquisition usually requires 2-7 minutes, limiting the temporal resolution of the measurement, see Borer J S, Bacharach S L, Green M V, et al: Real-time radionuclide cineangiography in the noninvasive evaluation of global and regional left ventricular function at rest and during exercise in patients with coronary artery disease, New Eng J Med 296:839-844, 1977; Pierson R N, Friedman M I, Tansey W A, et al: Cardiovascular nuclear medicine: an overview, Sem in Nucl Med 9:224-240, October 1979; and Brady T J, Thrall J H, Clare J M, et al: Exercise radionuclide ventriculography: practical considerations and sensitivity of coronary artery disease detection, Radiology 132:697-702, 1979.
Patients with atrial fibrillation or other cardiac arrythmias present timing problems in developing an accurate composite cardiac cycle. First-transit techniques require multiple injections if information is to be obtained for more than 4-7 cardiac cycles or during a prolonged observation period. The high count rates required by the first-transit technique are obtainable only on the multicrystal or the new "digital" camera, see Pierson R N et al cited supra, and see also Grenier R P, Bender M A, Jones R H: A computerized multi-crystal scintillation gamma camera, In Instrumentation in Nuclear Medicine, Vol. 2, Hine G J and Sorenson J A, Ed., New York, Academic, 1974, pp 101-134; Genna S, Pang S, Smith A: Digital scintigraphy: principles, design and performance, J Nucl Med 22:365-371, 1981; Lewellen T K, Murano R: A comparison of count rate parameters in gamma cameras, J Nucl Med 22:161-168, 1981; Adams R, Hine G J, Zimmerman C D: Deadtime measurements in scintillation cameras under scatter conditions simulating quantitative nuclear cardiology, J Nucl Med, 19:538-544, 1978; and Perry J R, Johnston R E, Hodge J R, et al: Digital gamma camera performance characteristics, J Nucl Med, 22:P66, 1981 (abst).
The nonimaging probe can record ejection fraction, relative cardiac output, and stroke volume every 30 seconds and reportedly can monitor beat-to-beat changes, see Camargo E E, Harrison K S, Wagner H N, et al: Noninvasive beat-to-beat monitoring of left ventricular function by a nonimaging nuclear detector during premature ventricular contractions, Am J Cardiol 45:1219-1224, 1980; Berger H J, Davies R A, Batsford W P, et al: Beat-to-beat left ventricular performance assessed from the equilibrium cardiac blood pool using a computerized nuclear probe, Circ 63:133-142, 1981; and Bacharach S L, Green M V, Borer J S, et al; Beat-by-beat validation of ECG gating, J Nucl Med 21:307-313, 1980. However, accurate identification of the left ventricle with a nonimaging system is difficult in many patients and motion artifacts may limit the accuracy of such a technique for beat-to-beat measurements.
Among the prior art patents relative to collimators and special purpose cameras may be mentioned U.S. Pat. Nos. 3,011,057; 3,060,316; 3,238,371; 3,710,119; 4,027,167; 4,086,494; 4,118,632; 4,129,784; 4,200,803; 4,202,612; 4,221,971; 4,266,135; 4,266,139; 4,293,771; 4,324,979.